Passing arguments from .launch file to .yaml file

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Hello, I am having problems with passing an argument into a .yaml file.

The problem is this:

map_type: costmap
observation_sources: scan
scan: {sensor_frame: $(arg namespace)/base_scan, data_type: LaserScan, topic: $(arg namespace)/scan, marking: true, clearing: true}

I am passing the argument, "BotN" for N robots in the launch file, e.g:

  <include file="$(find deploy)/launch/make_robot.launch" >
    <arg name="model"          value="burger"/>
    <arg name="namespace"      value="Bot1" />
    <arg name="initial_pose_x" value="-2.5"/>
    <arg name="initial_pose_y" value="4.0"/>
  </include>

But I get an insanely long error that doesn't really outline the issue.

Writing this in the .yaml file works, but I need it to work for multiple robots

scan: {sensor_frame: Bot1/base_scan, data_type: LaserScan, topic: Bot1/scan, marking: true, clearing: true}

Any idea?